Int 21 Fn 58  - DOS 5+ - Get Or Set Umb Link State                         [D]

   AH = 58h
   AL = subfunction
       02h get UMB link state

       Return: AL = 00h UMBs not part of DOS memory chain
              = 01h UMBs in DOS memory chain
       03h set UMB link state
       BX = 0000h remove UMBs from DOS memory chain
          = 0001h add UMBs to DOS memory chain

Return: CF clear if successful
   CF set on error
       AX = error code (01h) (see AH=59h)

Note:  a program which changes the UMB link state should restore it before
     terminating